If x is a proverb, then y=: x f. is equivalent to it,
except that any names that occur in the definition of x
are (recursively) replaced by their referents.
Consequently, any subsequent change in these referents that might
change the definition of x will not affect the definition
of y .

If x is the name of any entity (that is, a pronoun,
proverb, pro-adverb, or pro-conjunction), then 'x' f. is equivalent,
but with all names in its definition recursively replaced
by their referents.